Update - Added the translation of the original article, thanks to Treeston!

Patch 4.3 - Deathwing, Transmogrifier, Void Storage
Tom Chilton (Kalgan) answered a couple of questions from Gamona.de on Patch 4.3, and we got a bunch of very interesting news out of it. Patch 4.3 will feature:

New Raid - The Deathwing raid, making it very likely to be the last patch before the next expansion.

3 new 5-man instances - Including one in the Caverns of Time. (War of the Ancients was mentioned as a cataclysm instance a few years ago, but a lot of things have changed since then, who knows!)

The Transmogrifier NPC, which will let you change the appearance of any armor piece on you, while retaining the stats of your current gear. (= T12 stats, but with the Tier 2 look!)

Players won't be able to change the appearance of their armor into another armor type or class armor set, and you might have to own the armor before you can use it to swap the appearance of your existing armor.

The Void Storage is a new type of bank where players will be able to store their old armors in order to free up space in their regular bank.

The Abyssal Maw dungeon is gone for the moment, the storyline wasn't convincing enough/fitting.

If someone feels like adding information or even translating the article completely, post in comments!

Translation of the original article on gamona.de
We're at GamesCon in Cologne, Germany, and just did an interview with Tom Chilton, Lead Game Developer and Chris Robinson, Lead Art Director, in which they revealed a lot of details regarding patch 4.3 - and it seems that the announcement of it being huge was no joke:

Patch 4.3 will bring us the Deathwing raid instance! This means it's likely that we'll be able to fight the Aspect of Death in an epic encounter within this year. The raid that was originally expected for this patch, the "Abyssal Maw", was cut from the schedule because, as Chilton states, the setting and the story were not convincing enough.

Furthermore, 4.3 will also bring three entirely new 5-man instances - Chilton assured us that these won't contain any re-vamped content, but instead be brand new with unique design and models. Chilton also hinted at one of those being within the Caverns of Time, allowing players to experience another great moment of Warcraft Lore first-hand.

The interview also revealed the purpose of the "mystery ethereals" in Stormwind (and likely other cities, too). The "Transmogrifier" NPC will allow players to change the displayed model of equipment to that of another item while keeping the original attributes: Transmogrification is only possible within an armor class - Plate armor can only assume the looks of other Plate armor, for example.

The developers are considering whether they should only allow using the models of equipment that has already been obtained

The "Void Storage" is a very large bank-esque storage which allows old equipment to be stored, freeing up inventory/bank slots for players. The developers aren't sure yet about the definition of "old equipment". The cost of the storage (and whether there even is one) is another thing that is not yet decided

Another possible feature that was hinted at is the possibility of "void stored" equipment being available to other characters on the account (NOTE: That part might be speculation from Gamona, not cross-server transfers actually confirmed. Hard to tell.)

Overall, it seems that we've got a huge patch ahead of us - a new raid, three brand new instances, Transmogrification and Void Storage.

Nothing new really to add from the article boubouille, you've covered all the information there. The only thing I'd say is that they state the new instances are "completely new areas", so not a rehash like ZG/ZA, or the example they used, AQ.

I really get mixed feelings.
- the appearance is awesome but in PvP one will be fucked...
- 4.3 being Deathwing so the patch comes out like nov/dec 2011 and next expansion a year after? It better have 40 bosses...
- New 5mans - awesome. Those in ICC were great too. However I hope they add normal/heroic version and the HC one is really tuned for like 375+ people.

This will be so retarded so we get an expansion that lasts for Wat 1 year??? if this is the last patch Cata will get then i will recall all the bad words that i ever said about Wotlk .
The best mmo on the market is starting to look like a god damn joke.

OMG OMG OMG!!!! new 5 mans! HECK YEAH! T12 that I can make look like my T6.... HECK YEAH! Killing Deathwing... HECK YEAH! my only hope is that none of the new 5mans is rehashed content like a redone Kara or something like that

So 2 of their previous raid ideas are either gone or now 5 mans. For content this expansion has been utter tripe. If they do not make the Deathwing instance amazing, and not a collection of 7 bosses that feature incredibly frustrating mechanics, then Cataclysm will have failed.

OMG OMG OMG!!!! new 5 mans! HECK YEAH! T12 that I can make look like my T6.... HECK YEAH! Killing Deathwing... HECK YEAH! my only hope is that none of the new 5mans is rehashed content like a redone Kara or something like that

Highly likely the 5-mans are gonna be directly tied into the Deathwing raid. Like FoS, PoS and HoR were tied to LK